Torsion springs are known in the art which are provided as basic mechanical elements for resisting rotational motion. Torsion springs can be used for a variety of purposes including storage of energy, exerting torque within a mechanical system, providing flexibility for a mechanical system, and providing power for machines such as clocks and "wind-up" toys.
Each torsion spring, depending on the materials from which it is formed and its geometrical configuration, has a spring rate. The spring rate is usually substantially constant over the operating range of the spring. The spring rate represents how much torque is required to angularly displace ends of the torsion spring with respect to each other. The larger the spring rate, the greater the torque required to angularly displace the ends of the torsion spring.
In the design of mechanical systems which include torsion springs, a torsion spring is selected having a spring rate which produces the desired characteristics for the mechanical system. Often, the optimal spring rate for the mechanical system is not constant, but rather is a variable quantity. Torsion springs are known in the art which have a variety of different spring rates. However, each spring geometry and material configuration results in a unique, substantially constant spring rate. Accordingly, the machine designer selecting from prior art torsion springs must compromise and select a torsion spring which may not be optimal for all modes of operation of the machine incorporating the torsion spring. Accordingly, a need exists for a torsion spring having a spring rate which is adjustable to provide optimum performance characteristics over a broader range of operating conditions.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
______________________________________ U.S. Pat. No. ISSUE DATE INVENTOR ______________________________________ 4,155,547 May 22, 1979 Savio, et al. 4,900,019 February 13, 1990 Shamir 4,907,506 March 13, 1990 Davis, et al. 4,912,783 April 3, 1990 Shafer 5,176,370 January 5, 1993 Yamamoto ______________________________________